Immunology

摘要

As with previous Immunology sections of Current Opinion in Gasfroenterology, we have selected topics in immunology that reflect current active areas of investigation as well as selections that should be helpful to the gastroen-terologist in understanding mechanisms of gastrointestinal and liver disease states. In addition, we provide new observations in mucosal immunology that help explain the importance of gut flora in both health and in disease. In this edition, five topics are reviewed, two addressing the role of innate immunity in gastrointestinal and liver disease and one defining why we are not in chronic state of inflammation due to downregulation of inflammatory stimuli. Two additional reviews define the role of immune mechanisms in intestinal secretory states and epithelial necrosis. Finally, we review the expanding field of intestinal stem cells in gut immune development.In the mid-eighties, the term "immunophysiology of the gut" was popularized [1]. This concept suggested an interrelationship among the gut epithelium, the mucosal immune system, and other structures within the gut, (eg, enteric nervous system, to provide and integrated mucosal host defense) [2]. An example of the association is the role of cytokines in gastric acid production and in stimulating excessive fluid and electrolyte secretion [4]. More recently, we have recognized that this integrated system is further affected by the microbiota that colonize the gut. The term "bacterial epithelial cross talk" implies a reciprocal communication between bacteria (pathogens and commensals) and the gut epithelium [5]. For example, a colonizing bacterium can stimulate the upregu-lation on the enterocyte surface of its own receptor [6]. In addition, pathogens or commensal flora can activate enterocyte signal transduction pathways that either open or strengthen tight junctions [7]. Both the immunophysiology and microbial epithelial immunocyte "cross talk" are illustrated in reviews provided in this issue of Current.